1. Field of the Invention
The present invention relates to a fluid-filled elastic engine mount adapted to mount a power unit of a motor vehicle on a suitable support member of the vehicle in a vibration damping manner. More particularly, the present invention is concerned with such a fluid-filled elastic engine mount having an improved constructional arrangement, which is capable of exhibiting an excellent vibration damping effect with respect to engine idling vibrations, on the basis of flows of a fluid contained therein.
2. Discussion of the Prior Art
As one type of an engine mount which is interposed between a power unit such as an internal combustion engine of a motor vehicle and a support member so as to mount or support the power unit on the support member in a vibration damping manner, there is known a fluid-filled elastic engine mount wherein a first and a second mounting member which are respectively attached to one and the other of the power unit and the support member are spaced apart from each other by a suitable distance and are elastically connected to each other by an elastic body. The engine mount has a pressure-receiving chamber which is partially defined by the elastic body, and an equilibrium chamber which is partially defined by a flexible diaphragm. These pressure-receiving and equilibrium chambers are filled with a suitable non-compressible fluid, and communicate with each other by an orifice passage. A pressure of the fluid in the pressure-receiving chamber changes due to elastic deformation of the elastic body upon application of vibrations to the engine mount, while a volume of the equilibrium chamber is easily variable by displacement of the flexible diaphragm. This type of fluid-filled elastic engine mount is capable of exhibiting a high damping and isolating effect with respect to vibrations applied between the first and second mounting members, based on flows or resonance of the fluid which is forced to flow through the orifice. For this reason, the elastic mount of this type is favorably used as an engine mount for a motor vehicle, for example.
Generally, an engine mount is required to exhibit different damping or isolating characteristics depending on the type of the input vibrations having different frequencies and amplitudes. For instance, the engine mount for the motor vehicle is especially required to exhibit damping effects with respect to medium-frequency vibrations of several tens of Hz such as engine idling vibrations applied to the engine mount during idling of the vehicle while the vehicle is in a stop with the engine in an idling state, and with respect to low-frequency vibrations of about 10 Hz such as engine shakes applied to the engine mount during running of the vehicle. To meet the above requirement, the conventional engine mount is provided with two orifices between the pressure-receiving and equilibrium chambers, one of which is tuned to a medium frequency range corresponding to the engine idling vibrations and the other of which is tuned to a low frequency range corresponding to the engine shakes.
In view of a recently increasing requirement for improved smooth running stability of the vehicles, there has been an increasing demand for further improved damping or isolating characteristics of the engine mount. In particular, the engine mount is required to exhibit significantly improved damping or isolating characteristics with respect to the engine idling vibrations in order to minimize the vibrations and noise while the vehicle is stationary with the engine placed in its idling state.